In the processing of fabrics, both knitted and woven, an important characteristic of the fabric is the number of yarns or stitches per unit of length, particularly in the length direction. These characteristics can change significantly during fabric processing and thus can and do reflect the influence of the processing.
Because of the importance of monitoring fabric characteristics during processing, numerous attempts have been made to evaluate fabric characteristics on a real time basis, without stopping or otherwise interfering with the processing operations.
One known system for monitoring fabric condition involves the use of an optical device capable of counting the number of yarns or stitch courses passing by an optical sensing element during fabric processing. This device is utilized in combination with a measuring wheel, maintained in contact with the fabric, to determine the linear rate of fabric passage. By combining the linear rate of fabric passage with the count of the stitch courses, a relative measure of stitch courses per linear unit can be derived.
Another known system for measuring fabric characteristics involves the use of an imaging camera arranged to take and store an image of the fabric, and to electronically analyze the stored image to ascertain fabric characteristics. The last described system has advantages over that first described, in that it does not require physical contact with the fabric. Nevertheless, the latter system has important shortcomings, in that it is quite costly and has important limitations in relation to the information derived therefrom.
In accordance with the present invention, a novel and improved system is provided for analyzing fabric characteristics on a real time, in-process basis, in a manner to provide a more accurate and more useful measurement of fabric characteristics than has been available using prior art systems. In this respect, fabrics being handled on processing lines, both woven and knitted, but particularly knitted fabrics, can become considerably skewed in the course of processing such that, for example, their stitch courses, in the case of knitted fabrics, or warp yarns, in the case of woven fabrics, are not perpendicular to the longitudinal axis of the fabric. Additionally, even if the yarns or stitch lines are symmetrical with respect to the longitudinal axis, the cross lines of the fabric may become bowed, with the center portion of the fabric either leading or lagging the edge portions. The method and system of the present invention enable these skewed conditions to be both detected and evaluated. This not only enables in-process correcting adjustments to be made on a real time basis, but also enables greater accuracy to be realized in the determination of the number of stitches per unit of length, because such determination takes into account the existing skew condition of the fabric.
Pursuant to the present invention, a digitized freeze-frame image of the fabric is taken and stored, and then analyzed electronically. As a particular feature of novelty, the method and system of the present invention involves initially examining the freeze-frame image along a series of axes, each slightly angularly displaced from the other. By comparison of these several analyses, it is possible to identify lines of stitches in the fabric (hereinafter referred to generically as construction lines of the fabric) regardless of angularity thereof. Having thus identified the orientation of the fabric construction line, in relation to the orientation of the digitized image, the image is then electronically analyzed along lines parallel with and/or at right angles to the identified construction line. Out of this analysis is derived not only a highly accurate stitch count, but also a quantitative measure of the skew angle of the fabric construction line.
By using a plurality of imaging cameras located across the width of a moving fabric web, or a traversing camera arrangement for taking and processing successive images across the width of the fabric, it is also possible to detect and quantify bowing of the fabric across its width.
In known systems for obtaining digitized, freeze-frame images of a fabric for analyzing construction characteristics, it is known to utilize infrared light sources, as a means of minimizing any sensitivity of the imaging apparatus to changes in colors of the fabric passing underneath. While this arrangement is quite effective, it is somewhat costly. In accordance with the present invention, a conventional xenon strobe unit can be utilized to provide light energization for the imaging camera. However, the imaging source is filtered to substantially eliminate light in the visible range, so that the remaining light, capable of energizing the imaging camera, is the near infrared and infrared ranges. The arrangement efficiently achieves insensitivity to color changes in the fabric, but with greater simplicity and at a significantly lower cost than using conventional infrared technology.
Overall, the system of the invention enables a higher degree of precision to be achieved in the determination of fabric characteristics, enables skew conditions to be detected and quantified, and at the same time may be provided at a significantly lower cost than the known systems currently available.
For a more complete understanding of the above and other features and advantages of the invention, reference should be made to the following detailed description of a preferred embodiment of the invention, and to the accompanying drawings.